As integrated circuit devices decrease in size, the space available for wiring the device and a space between wirings within the device also decrease. For example, in order to form a contact that connects isolated device areas to each other through a highly conductive thin film, an aligning margin and a device isolation margin are typically utilized, thus a relatively large space is conducive to forming the integrated circuit device.
In a memory device, such as a Dynamic Random Access Memory (DRAM), the size of the contact is a factor used to determine the size of the memory cell. Recently, a manufacturing technique has been developed for manufacturing integrated circuit devices having a size of, for example, less than about 0.25 μm. It is typically difficult to form a fine contact using conventional fabrication methods. Furthermore, in memory devices having a plurality of conductive layers, the spacing between conductive layers is typically increased by the presence of an insulating layer interposed therebetween, thus possibly making it difficult to form the contact between the conductive layers. Therefore, in memory cells having a compact design and repeating patterns, self-aligned contacts are typically used to reduce the cell area.
A self-aligned contact is typically formed using step differences of peripheral structures. Various contacts may be obtained without using a mask by using the height of the peripheral structure, the thickness of an insulation film in a predetermined area where the contact is formed, and an etching method. A possible advantage of the self-aligned contact technique is that a fine contact can be formed without an aligning margin. A conventional self-aligned contact technique typically has a contact hole that is formed using an anisotropic etching process using an etching selectivity between an oxide film and a nitride film.
Now referring to FIGS. 1A and 1B, cross-sectional views of conventional integrated circuits having self-aligned contacts will be discussed below. Referring to FIG. 1A, a MOS transistor (not shown) is formed on an microelectronic substrate 10 having an active area defined by a field oxide film 12. A first insulating layer 14 consisting of silicon oxide is formed by depositing silicon oxide on the surface of the microelectronic substrate 10. A conductive layer for a bit line BL and a second insulating layer consisting of silicon nitride are deposited on the first insulating layer 14. A photolithography process is carried out for patterning the second insulating layer and the conductive layer, so that bit line structures BL consisting of a second insulation film pattern 18 and a bit line 16 are formed. Silicon nitride is deposited on the surface of the resulting structure thereby forming a silicon nitride layer. The silicon nitride layer is anisotropically etched so as to form a spacer 20 consisting of silicon nitride on the sidewalls of the bit line structure BL.
Now referring to FIG. 1B, a third insulating layer 22 consisting of silicon oxide is formed by depositing silicon oxide on the surface of the resulting structure. A photoresist pattern (not shown) is formed in such a manner that a contact hole larger than the space between the bit line structures BL can be defined. The third insulating layer 22 is etched by an anisotropic etching process using the etching selectivity between a silicon oxide film and a silicon nitride film, thereby forming a storage node contact hole 24 for exposing a substrate area between the bit line structures BL. The photoresist pattern is used as an etching mask. A capacitor electrode (not shown) may be provided to bury the node contact hole 24.
The silicon nitride film may be used as the spacer 20, which is formed at the sidewall of the bit line structure BL, and the silicon oxide film may be used as the third insulating layer 22. However, since the bond energy of the silicon oxide film may be greater than the bond energy of the silicon nitride film, it may be difficult to increase the etching selectivity between the silicon oxide film and the silicon nitride film as the size of the storage node contact hole 24 decreases.
Typically, a predetermined space is provided between the bit line structures BL, i.e. storage node contact hole 24, by using the self-aligned contact process. If the width of the sidewall spacer 20 is reduced to increase the spacing, the sidewall spacer 20 may be consumed during the etching process for forming the self-aligned contact. Thus, a short may occur. Alternatively, if the width of the sidewall spacer 20 is increased, it may be difficult to bury a gap formed between the bit line structures BL as discussed above.
In addition, the sidewall spacer 20, consisting of silicon nitride, typically has a dielectric constant above 7. Thus, the parasitic capacitance between the bit lines may be twice the parasitic capacitance of the conventional contact structure in which the bit line is insulated from the storage electrode by using the silicon oxide film having the dielectric constant of 3.9.
Recently, to address the short comings of existing conventional structures, a method for forming the sidewall spacer in the contact hole after forming the self-aligned contact while preventing a short between the storage electrode and the bit line has been discussed. For example, this method is discussed in Japanese Patent No. JP9097880A2 entitled Semiconductor Storage Device and Its Manufacture to Hirosuke et al.
Now referring to FIGS. 2A and 2B, cross-sectional views of integrated circuits illustrating the method for manufacturing a DRAM cell disclosed in the above referenced Japanese Patent will be discussed. A field oxide film 52 is formed on a microelectronic substrate 50 by using a shallow trench isolation (STI) technique. A conventional MOS transistor manufacturing process is carried out so as to form a MOS transistor consisting of a gate region and a source/drain region on the surface of the substrate 50.
Silicon oxide is deposited on the surface of the microelectronic substrate 50 forming a silicon oxide film 54. A contact hole for exposing the source/drain region is formed by using a self-aligned contact process. A pad electrode 56 for burying the contact hole is formed at the same height as the gate. Silicon oxide is deposited on the surface of the resulting structure, thereby forming a first insulating layer 58.
A conductive layer for a bit line, a second insulating layer consisting of silicon oxide, and a third insulating layer consisting of silicon nitride are sequentially formed on the first insulating layer 58. The third insulating layer, the second insulating layer and the conductive layer are subject to a photolithography process, so that bit line structures BL consisting of a third insulating layer pattern 64, a second insulating layer pattern 62 and a bit line 60 are formed.
Referring now to FIG. 2B, a fourth insulating layer 66 is formed by depositing silicon oxide on the resulting structure. The fourth insulating layer 66 is planarized by performing a chemical mechanical polishing (CMP) process. The third insulation pattern 64 may be used as a stopper.
Referring now to FIG. 2C, the fourth insulating layer 66 is etched using the high etching selectivity between the silicon oxide film and the silicon nitride film. The first insulating layer 58 formed on the pad electrode 56 is simultaneously etched so that a first insulating layer pattern 58a is formed. At the same time, a storage node contact hole 68, which is self-aligned with respect to the bit line structure BL, is formed.
Referring now to FIG. 2D, a thin silicon oxide film is formed by depositing silicon oxide on the surface of the resulting structure. The silicon oxide film is anisotropically etched so that a spacer 70 is formed in the storage node contact hole 68. A storage electrode (not shown) of a capacitor for burying the storage node contact hole 68 may be formed.
The conventional method discussed with respect to FIGS. 2A through 2D may address some of the problems discussed with respect to the methods and devices of FIGS. 1A through 1B. For example, the gap burying problem caused by the spacer 70 may be improved by forming spacer 70 after forming the storage node contact hole 68 and the increase in the parasitic capacitance between the bit lines 60 may be improved by fabricating the spacer 70 using a silicon oxide film having a low dielectric constant. However, if the bit line structure BL has an inclined profile, the height of the spacer 70 may be lowered, thus, a part of the bit line 60, i.e. an upper end portion of the bit line 60 may be exposed, thus, a short may occur between the bit line 60 and the storage electrode.